As disclosed in Matsui et al., Chemistry Letters, 1981, pp. 1719-1720, it is known that aromatic iodides can be trifluoromethylated by reacting them with a large excess of sodium trifluoroacetate in the presence of cuprous iodide and a dipolar aprotic solvent. Matsui et al. also show that some trifluoromethylation occurs when an aromatic bromide is employed in the reaction instead of an iodide but that the yield of product is quite low.
Copending application Ser. No. 724,474 (Ramachandran et al.), filed Apr. 18, 1985, now U.S. Pat. No. 4,590,010, teaches that the technique of Matsui et al. is applicable to the trifluoromethylation of 6-alkoxy-5-halo-1-cyanonaphthalenes and the corresponding naphthoate esters--compounds which, like the compounds of Matsui et al., give better yields of the desired products when the halo substituent is iodo. Ramachandran et al. indicate that other trifluoroacetate salts can be used in their process, but they disclose a preference for using sodium trifluoroacetate as the trifluoromethylating agent.
It has been found that the use of sodium trifluoroacetate as a trifluoromethylating agent has several disadvantages. As mentioned above, sodium trifluoroacetate has to be used in considerable excess, and it does not provide acceptable yields of product from aromatic bromides. Moreover, its use requires a longer reaction time than would be desired, and it leads to the formation of relatively large amounts of by-products.